This invention relates to a low friction sheet for use with a tape roll. By the term "tape roll" as used in this invention is meant long, flexible, band-like members (also referred to simply as "tapes"), such as magnetic tapes, e.g., video tapes, audio tapes, etc., and movie films, e.g., Single 8, Super 8, etc., which are wound in the form of roll.
Tape roll materials are typically placed in a case, usually referred to as a cassette, magazine, or cartridge, and wound or rewound in the inside thereof. During such winding or rewinding, the friction between the tape roll and the internal surface of the case may prevent the tape from winding smoothly. In general, therefore, a low friction member, referred to as a friction sheet is placed fixedly or rotatably between the internal surface of the case and the tape roll.
This friction sheet, therefore, is required to have a low coefficient of friction, have good abrasion resistance and dimensional stability, and furthermore, may be desired to have static electrification-preventing properties.
Friction sheets heretofore known include a fluorine resin sheet, silicone materials, wax coated paper, a sheet as disclosed in Japanese Patent Application (OPI) No. 145482/75, which is prepared by incorporating a fluorine compound into the surface of a thermoplastic film, and a sheet as disclosed in Japanese Utility Model Publication No. 2858/68, which is prepared by coating at least one of wax, low molecular weight polyethylene and a sodium salt of alkyl sulfate onto the surface of a paper.
Such friction sheets, however, have not been completely satisfactory with respect to abrasion resistance and surface stability. Those sheets containing fluorine have the disadvantage that their production costs are high because their moldability is poor and the materials per se are expensive.
Furthermore, friction sheet known in recent years includes a sheet composed of polyethylene film, wherein the polyethylene has a molecular weight of at least several million, and calls an ultra-high molecular weight polyethylene. The moldability of ultra-high molecular weight polyethylene is extremely poor due to the ultra-high molecular weight. Therefore, the friction sheets are prepared by at first obtaining a molding in the form of rod of which section perpendicular to longitudinal direction of the molding is a shape desired for the objective friction sheets; and then cutting the molding into round slices in a thickness desired for the objective friction sheets.
Such friction sheet, however, also has the disadvantage that its production cost is extremely high (about 10 times higher than the production cost of friction sheet of the present invention) because the method for preparing the friction sheets is complicated.
According to the above method, the ultra-high molecular weight polyethylene film is not oriented.